The trailer hitch which is most commonly available comprises a single hitch ball secured in a fixed position to the rear of a vehicle. In order to hook up to a trailer, the trailer itself must be moved to a connecting position with the hitch ball. This can be awkward, particularly in the case of very heavy trailer, and in addition can be dangerous if the trailer is not sitting on level ground in which case the trailer may have a tendency to roll at the person who is trying to move it.
These problems associated with conventional fixed trailer balls have been appreciated and recognized by earlier inventors. For example, U.S. Pat. No. 3,126,210 to Hill describes a trailer hitch with a draw bar which is adjustable transversely and longitudinally of the hitch. However, the structure in this patent would only fit interiorly of a truck bed and even then requires modifications in the form of a specifically created opening in the rear panel of the truck bed.
According to Hill, the initial hook up of the trailer ball to the trailer is facilitated by adjusting the draw bar. From there, the draw bar and trailer are moved to the towing position by moving the truck around to reposition the draw bar. This method of connection is based on the often incorrect assumption that the trailer will react in a prescribed pattern according to the motion of the truck. However, in many cases, the trailer will roll back, forward or jump from side to side as the terrain dictates. Furthermore, on smooth ground, the friction of the mechanism in the hitch may be greater than the rolling resistance of the trailer making it very difficult to get the truck and the trailer to line up in the towing position.
U.S. Pat. No. 2,745,680 discloses a tractor hitch having a hitch bar which can be pulled rearwardly and swung sideways of the tractor to hook up to an implement to be towed by the tractor. Once again, final maneuvering to the towing position is achieved by backing the tractor up to the implement.
U.S. Pat. No. 4,773,667 discloses a trailer hitch having a boom which is both extendable and swingable to different hook up positions, however, the swing and extension movements of the hitch bar are not independent of one another because the rear end of the hitch bar is on a cam follower. This limits the number of positions to which the hitch bar can be moved because it's sideways angled position is dictated by it's extended positioning and vis-a-versa.
The interaction of the length adjustment and sideways positioning of the structure in the '667 patent may also make it difficult to manually move the trailer since the trailer has to both be moved towards center and be drawn inwardly in a single manual movement of the hitch.
U.S. Pat. No. 4,744,583 discloses a trailer hitch having a hitch bar which is both extendable and swingable relative to the hitch. As is the case with the structure in U.S. Pat. No. 4,773,667 the swinging and extension motions are tied in with one another. Therefore, once again, the structure in the '583 patent suffers from the drawback that the hitch bar can only be moved to a relatively limited number of positions. It does not however suffer the difficulties associated with drawing the trailer into the towing position because the hitch in the '583 patent is motorized. On the other hand, a motorized tow hitch is substantially more costly than a manually operated hitch.